chat : Deepseek V3.1 reasoning and tool calling support (OpenAI Style) (#15533)

* Add DeepSeek V3.1 thinking mode support

- Added COMMON_CHAT_FORMAT_DEEPSEEK_V3_1 enum value
- Created common_chat_params_init_deepseek_v3_1() function (currently uses R1 implementation)
- Created common_chat_parse_deepseek_v3_1() function that handles V3.1 thinking format:
  - Extracts reasoning content before '</think>' tag into reasoning_content
  - Extracts regular content after '</think>' tag into content
  - No opening '<think>' tag in V3.1 format
- Added detection logic for V3.1 templates based on pattern: 'message['prefix'] is defined and message['prefix'] and thinking'
- Added V3.1 case to parsing switch statement

This addresses the issue where V3.1 outputs reasoning content followed by '</think>' and then regular content without the opening '<think>' tag.

* Another attempt by V3.1 non-thinking

* Fix test, but it's not asserting anything.

* Ignore vim swap files in tests dir

* Update the test

* Try using try_find_literal instead of regex

* passing test

* Revert "Try using try_find_literal instead of regex"

This reverts commit c50d887.

* Remove unnecessary change

* Remove comment

* Add code to handle non-thinking mode.

* Try to set message['prefix'] when thinking is enabled.

* This fixes reasoning, but breaks normal content. We need state in the
chat parser.

* DeepSeek V3.1 thinking is now the default. Disable with `--reasoning-budget 0`.

* Simplify (DeepSeek V3.1 reasoning)

* Fix sign inversion bug

* Add some tool calling code (not working).

* Tool calls working in non-reasoning mode.

* Attempt a unit test for tool call parsing.

* Passing test

* Add tests for both happy path and broken fenced DeepSeek V3.1 tool call variants.

* Passing DeepSeek V3.1 tool call tests, but model is not working.

* Revert assistance response prefill change. Not my monkeys.

* Add fenced_thinking unit test variant. Passes, but thinking tool calling
still isn't working for some reason.

* Tests pass in reasoning mode. Also e2e tool test passes.

* Make a copy of the parse_json_tool_calls function for deepseek-v3.1 so
as to not accidentally introduce regressions.

* Fix thinking_forced_open logic. tool calling broken. Need to add another
test case.

* That's what I get for cargo culting a newline.

* Add multi tool call test for deepseek v3.1 non-reasoning

* Move test, remove .gitignore change

* Place deepseek-v3.1 reasoning test directly into existing reasoning
function per CISC's request.

* Address whitespace CI failure.

* Merge two assert_equals per CISC's request.

* Add DeepSeek-V3.1 tests to tests/test-chat.cpp per CISC's request.

* Merge deepseek V3.1 and regular parse_json_tool_calls() function
behaviors by adding optional update_cursor argument.

* Update tests/test-chat-parser.cpp

Co-authored-by: Sigbjørn Skjæret <[email protected]>

* Update tests/test-chat-parser.cpp

Co-authored-by: Sigbjørn Skjæret <[email protected]>

* Update tests/test-chat-parser.cpp

Co-authored-by: Sigbjørn Skjæret <[email protected]>

* Update tests/test-chat-parser.cpp

Co-authored-by: Sigbjørn Skjæret <[email protected]>

* Update tests/test-chat-parser.cpp

Co-authored-by: Sigbjørn Skjæret <[email protected]>

* Update tests/test-chat-parser.cpp

Co-authored-by: Sigbjørn Skjæret <[email protected]>

* Update tests/test-chat-parser.cpp

Co-authored-by: Sigbjørn Skjæret <[email protected]>

* Update tests/test-chat-parser.cpp

Co-authored-by: Sigbjørn Skjæret <[email protected]>

* Update tests/test-chat-parser.cpp

Co-authored-by: Sigbjørn Skjæret <[email protected]>

* DeepSeek V3.1 fix reasoning_format none

* Strip grammar down to strictly what we expect based on model card. Throw
out parts we cargo culted from R1 that don't make sense.

* Update tests/test-chat-parser.cpp

Co-authored-by: Sigbjørn Skjæret <[email protected]>

* DeepSeek V3.1 - Add edge case where thinking is forced open, there is
tool calling in the reasoning content, but then the model just stops the
output without closing the </think> tag, so it's not a partial. In this
case, use the tool call in the reasoning content.

* DeepSeek V3.1 - simplify update_cursor

* Update common/chat.cpp

Co-authored-by: Sigbjørn Skjæret <[email protected]>

* Update common/chat.cpp

Co-authored-by: Sigbjørn Skjæret <[email protected]>

* Update common/chat.cpp

Co-authored-by: Sigbjørn Skjæret <[email protected]>

* Fix indent

---------

Co-authored-by: openhands <[email protected]>
Co-authored-by: Sigbjørn Skjæret <[email protected]>

Author: 3 people

common/chat.cpp

@@ -631,6 +631,7 @@ const char * common_chat_format_name(common_chat_format format) {
         case COMMON_CHAT_FORMAT_FIREFUNCTION_V2: return "FireFunction v2";
         case COMMON_CHAT_FORMAT_FUNCTIONARY_V3_2: return "Functionary v3.2";
         case COMMON_CHAT_FORMAT_FUNCTIONARY_V3_1_LLAMA_3_1: return "Functionary v3.1 Llama 3.1";
+        case COMMON_CHAT_FORMAT_DEEPSEEK_V3_1: return "DeepSeek V3.1";
         case COMMON_CHAT_FORMAT_HERMES_2_PRO: return "Hermes 2 Pro";
         case COMMON_CHAT_FORMAT_COMMAND_R7B: return "Command R7B";
         case COMMON_CHAT_FORMAT_GRANITE: return "Granite";
@@ -698,11 +699,13 @@ static void parse_json_tool_calls(
         size_t from = std::string::npos;
         auto first = true;
         while (true) {
+            auto start_pos = builder.pos();
             auto res = function_regex_start_only && first
                 ? builder.try_consume_regex(*function_regex_start_only)
                 : function_regex
                     ? builder.try_find_regex(*function_regex, from)
                     : std::nullopt;
+
             if (res) {
                 std::string name;
                 if (get_function_name) {
@@ -737,6 +740,8 @@ static void parse_json_tool_calls(
                     return;
                 }
                 throw common_chat_msg_partial_exception("incomplete tool call");
+            } else {
+                builder.move_to(start_pos);
             }
             break;
         }
@@ -1388,6 +1393,71 @@ static common_chat_params common_chat_params_init_deepseek_r1(const common_chat_
     }
     return data;
 }
+
+static common_chat_params common_chat_params_init_deepseek_v3_1(const common_chat_template & tmpl, const struct templates_params & inputs) {
+    common_chat_params data;
+
+    // Pass thinking context for DeepSeek V3.1 template
+    json additional_context = {
+        {"thinking", inputs.enable_thinking},
+    };
+
+    auto prompt = apply(tmpl, inputs,
+                       /* messages_override= */ inputs.messages,
+                       /* tools_override= */ std::nullopt,
+                       additional_context);
+    data.prompt = prompt;
+    data.format = COMMON_CHAT_FORMAT_DEEPSEEK_V3_1;
+    if (string_ends_with(data.prompt, "<think>")) {
+        if (!inputs.enable_thinking) {
+            data.prompt += "</think>";
+        } else {
+            data.thinking_forced_open = true;
+        }
+    }
+    if (inputs.tools.is_array() && !inputs.tools.empty()) {
+        data.grammar_lazy = inputs.tool_choice != COMMON_CHAT_TOOL_CHOICE_REQUIRED && inputs.json_schema.is_null();
+        data.grammar = build_grammar([&](const common_grammar_builder & builder) {
+            std::vector<std::string> tool_rules;
+            foreach_function(inputs.tools, [&](const json & tool) {
+                const auto & function = tool.at("function");
+                std::string name = function.at("name");
+                auto parameters = function.at("parameters");
+                builder.resolve_refs(parameters);
+                tool_rules.push_back(builder.add_rule(name + "-call",
+                    "( \"<｜tool▁call▁begin｜>\" )? \"" + name + "<｜tool▁sep｜>"
+                    "\" " + builder.add_schema(name + "-args", parameters) + " "
+                    "\"<｜tool▁call▁end｜>\""));
+            });
+            // Distill Qwen 7B & 32B models seem confused re/ syntax of their tool call opening tag,
+            // so we accept common variants (then it's all constrained)
+            builder.add_rule("root",
+                std::string(data.thinking_forced_open ? "( \"</think>\" space )? " : "") +
+                "( \"<｜tool▁calls▁begin｜>\" | \"<｜tool_calls_begin｜>\" | \"<｜tool calls begin｜>\" | \"<｜tool\\\\_calls\\\\_begin｜>\" | \"<｜tool▁calls｜>\" ) "
+                "(" + string_join(tool_rules, " | ") + ")" + (inputs.parallel_tool_calls ? "*" : "") + " "
+                "\"<｜tool▁calls▁end｜>\""
+                " space");
+            data.grammar_triggers.push_back({
+                COMMON_GRAMMAR_TRIGGER_TYPE_PATTERN_FULL,
+                // If thinking_forced_open, then we capture the </think> tag in the grammar,
+                // (important for required tool choice) and in the trigger's first capture (decides what is sent to the grammar)
+                std::string(data.thinking_forced_open ? "[\\s\\S]*?(</think>\\s*)" : "(?:<think>[\\s\\S]*?</think>\\s*)?") +
+                    "(<｜tool▁calls▁begin｜>|<｜tool_calls_begin｜>|<｜tool calls begin｜>|<｜tool\\\\_calls\\\\_begin｜>|<｜tool▁calls｜>)[\\s\\S]*"
+            });
+            data.preserved_tokens = {
+                "<think>",
+                "</think>",
+                "<｜tool▁calls▁begin｜>",
+                "<｜tool▁call▁begin｜>",
+                "<｜tool▁sep｜>",
+                "<｜tool▁call▁end｜>",
+                "<｜tool▁calls▁end｜>",
+            };
+        });
+    }
+    return data;
+}
+
 static void common_chat_parse_deepseek_r1(common_chat_msg_parser & builder) {
     builder.try_parse_reasoning("<think>", "</think>");
     if (!builder.syntax().parse_tool_calls) {
@@ -1409,6 +1479,66 @@ static void common_chat_parse_deepseek_r1(common_chat_msg_parser & builder) {
         tool_calls_end);
 }
 
+static void common_chat_parse_deepseek_v3_1_content(common_chat_msg_parser & builder) {
+    static const common_regex function_regex("(?:<｜tool▁call▁begin｜>)?([^\\n<]+)(?:<｜tool▁sep｜>)");
+
+    static const common_regex close_regex("(?:[\\s]*)?<｜tool▁call▁end｜>");
+    static const common_regex tool_calls_begin("(?:<｜tool▁calls▁begin｜>|<｜tool_calls_begin｜>|<｜tool calls begin｜>|<｜tool\\\\_calls\\\\_begin｜>|<｜tool▁calls｜>)");
+    static const common_regex tool_calls_end("<｜tool▁calls▁end｜>");
+
+    if (!builder.syntax().parse_tool_calls) {
+        LOG_DBG("%s: not parse_tool_calls\n", __func__);
+        builder.add_content(builder.consume_rest());
+        return;
+    }
+
+    LOG_DBG("%s: parse_tool_calls\n", __func__);
+
+    parse_json_tool_calls(
+        builder,
+        /* block_open= */ tool_calls_begin,
+        /* function_regex_start_only= */ std::nullopt,
+        function_regex,
+        close_regex,
+        tool_calls_end);
+}
+
+static void common_chat_parse_deepseek_v3_1(common_chat_msg_parser & builder) {
+    // DeepSeek V3.1 outputs reasoning content between "<think>" and "</think>" tags, followed by regular content
+    // First try to parse using the standard reasoning parsing method
+    LOG_DBG("%s: thinking_forced_open: %s\n", __func__, std::to_string(builder.syntax().thinking_forced_open).c_str());
+
+    auto start_pos = builder.pos();
+    auto found_end_think = builder.try_find_literal("</think>");
+    builder.move_to(start_pos);
+
+    if (builder.syntax().thinking_forced_open && !builder.is_partial() && !found_end_think) {
+        LOG_DBG("%s: no end_think, not partial, adding content\n", __func__);
+        common_chat_parse_deepseek_v3_1_content(builder);
+    } else if (builder.try_parse_reasoning("<think>", "</think>")) {
+        // If reasoning was parsed successfully, the remaining content is regular content
+        LOG_DBG("%s: parsed reasoning, adding content\n", __func__);
+        // </think><｜tool▁calls▁begin｜><｜tool▁call▁begin｜>function<｜tool▁sep｜>NAME\n```json\nJSON\n```<｜tool▁call▁end｜><｜tool▁calls▁end｜>
+        common_chat_parse_deepseek_v3_1_content(builder);
+    } else {
+        if (builder.syntax().reasoning_format == COMMON_REASONING_FORMAT_NONE) {
+          LOG_DBG("%s: reasoning_format none, adding content\n", __func__);
+          common_chat_parse_deepseek_v3_1_content(builder);
+          return;
+        }
+        // If no reasoning tags found, check if we should treat everything as reasoning
+        if (builder.syntax().thinking_forced_open) {
+            // If thinking is forced open but no tags found, treat everything as reasoning
+            LOG_DBG("%s: thinking_forced_open, adding reasoning content\n", __func__);
+            builder.add_reasoning_content(builder.consume_rest());
+        } else {
+            LOG_DBG("%s: no thinking_forced_open, adding content\n", __func__);
+            // <｜tool▁call▁begin｜>NAME<｜tool▁sep｜>JSON<｜tool▁call▁end｜>
+            common_chat_parse_deepseek_v3_1_content(builder);
+        }
+    }
+}
+
 static common_chat_params common_chat_params_init_gpt_oss(const common_chat_template & tmpl, const struct templates_params & inputs) {
     common_chat_params data;
     auto prompt = apply(tmpl, inputs);
@@ -2365,6 +2495,12 @@ static common_chat_params common_chat_templates_apply_jinja(
         }
     }
 
+    // DeepSeek V3.1: detect based on specific patterns in the template
+    if (src.find("message['prefix'] is defined and message['prefix'] and thinking") != std::string::npos &&
+        params.json_schema.is_null()) {
+        return common_chat_params_init_deepseek_v3_1(tmpl, params);
+    }
+
     // DeepSeek R1: use handler in all cases except json schema (thinking / tools).
     if (src.find("<｜tool▁calls▁begin｜>") != std::string::npos && params.json_schema.is_null()) {
         return common_chat_params_init_deepseek_r1(tmpl, params);
@@ -2537,6 +2673,9 @@ static void common_chat_parse(common_chat_msg_parser & builder) {
         case COMMON_CHAT_FORMAT_DEEPSEEK_R1:
             common_chat_parse_deepseek_r1(builder);
             break;
+        case COMMON_CHAT_FORMAT_DEEPSEEK_V3_1:
+            common_chat_parse_deepseek_v3_1(builder);
+            break;
         case COMMON_CHAT_FORMAT_FUNCTIONARY_V3_2:
             common_chat_parse_functionary_v3_2(builder);
             break;

common/chat.h

@@ -107,6 +107,7 @@ enum common_chat_format {
     COMMON_CHAT_FORMAT_FIREFUNCTION_V2,
     COMMON_CHAT_FORMAT_FUNCTIONARY_V3_2,
     COMMON_CHAT_FORMAT_FUNCTIONARY_V3_1_LLAMA_3_1,
+    COMMON_CHAT_FORMAT_DEEPSEEK_V3_1,
     COMMON_CHAT_FORMAT_HERMES_2_PRO,
     COMMON_CHAT_FORMAT_COMMAND_R7B,
     COMMON_CHAT_FORMAT_GRANITE,

models/templates/README.md

@@ -22,4 +22,5 @@ These templates can be updated with the following commands:
 ./scripts/get_chat_template.py Qwen/QwQ-32B                                  > models/templates/Qwen-QwQ-32B.jinja
 ./scripts/get_chat_template.py Qwen/Qwen3-0.6B                               > models/templates/Qwen-Qwen3-0.6B.jinja
 ./scripts/get_chat_template.py zai-org/GLM-4.5                               > models/templates/zai-org-GLM-4.5.jinja
+./scripts/get_chat_template.py deepseek-ai/DeepSeek-V3.1                     > models/templates/deepseek-ai-DeepSeek-V3.1.jinja
 ```

models/templates/deepseek-ai-DeepSeek-V3.1.jinja

@@ -0,0 +1,3 @@
+{% if not add_generation_prompt is defined %}{% set add_generation_prompt = false %}{% endif %}{% if not thinking is defined %}{% set thinking = false %}{% endif %}{% set ns = namespace(is_first=false, is_tool=false, system_prompt='', is_first_sp=true, is_last_user=false) %}{%- for message in messages %}{%- if message['role'] == 'system' %}{%- if ns.is_first_sp %}{% set ns.system_prompt = ns.system_prompt + message['content'] %}{% set ns.is_first_sp = false %}{%- else %}{% set ns.system_prompt = ns.system_prompt + '
+
+' + message['content'] %}{%- endif %}{%- endif %}{%- endfor %}{{ bos_token }}{{ ns.system_prompt }}{%- for message in messages %}{%- if message['role'] == 'user' %}{%- set ns.is_tool = false -%}{%- set ns.is_first = false -%}{%- set ns.is_last_user = true -%}{{'<｜User｜>' + message['content']}}{%- endif %}{%- if message['role'] == 'assistant' and message['tool_calls'] is defined and message['tool_calls'] is not none %}{%- if ns.is_last_user %}{{'<｜Assistant｜></think>'}}{%- endif %}{%- set ns.is_last_user = false -%}{%- set ns.is_first = false %}{%- set ns.is_tool = false -%}{%- for tool in message['tool_calls'] %}{%- if not ns.is_first %}{%- if message['content'] is none %}{{'<｜tool▁calls▁begin｜><｜tool▁call▁begin｜>'+ tool['function']['name'] + '<｜tool▁sep｜>' + tool['function']['arguments'] + '<｜tool▁call▁end｜>'}}{%- else %}{{message['content'] + '<｜tool▁calls▁begin｜><｜tool▁call▁begin｜>' + tool['function']['name'] + '<｜tool▁sep｜>' + tool['function']['arguments'] + '<｜tool▁call▁end｜>'}}{%- endif %}{%- set ns.is_first = true -%}{%- else %}{{'<｜tool▁call▁begin｜>'+ tool['function']['name'] + '<｜tool▁sep｜>' + tool['function']['arguments'] + '<｜tool▁call▁end｜>'}}{%- endif %}{%- endfor %}{{'<｜tool▁calls▁end｜><｜end▁of▁sentence｜>'}}{%- endif %}{%- if message['role'] == 'assistant' and (message['tool_calls'] is not defined or message['tool_calls'] is none) %}{%- if ns.is_last_user %}{{'<｜Assistant｜>'}}{%- if message['prefix'] is defined and message['prefix'] and thinking %}{{'<think>'}}  {%- else %}{{'</think>'}}{%- endif %}{%- endif %}{%- set ns.is_last_user = false -%}{%- if ns.is_tool %}{{message['content'] + '<｜end▁of▁sentence｜>'}}{%- set ns.is_tool = false -%}{%- else %}{%- set content = message['content'] -%}{%- if '</think>' in content %}{%- set content = content.split('</think>', 1)[1] -%}{%- endif %}{{content + '<｜end▁of▁sentence｜>'}}{%- endif %}{%- endif %}{%- if message['role'] == 'tool' %}{%- set ns.is_last_user = false -%}{%- set ns.is_tool = true -%}{{'<｜tool▁output▁begin｜>' + message['content'] + '<｜tool▁output▁end｜>'}}{%- endif %}{%- endfor -%}{%- if add_generation_prompt and ns.is_last_user and not ns.is_tool %}{{'<｜Assistant｜>'}}{%- if not thinking %}{{'</think>'}}{%- else %}{{'<think>'}}{%- endif %}{% endif %}