feat: add Anthropic extended thinking support (#278)

* add thinking capabilities for Anthropic models

* remove redundant header

* clean up thinking determination logic

* cleaner way of keeping track of thinking state

* disable anthropic thinking for topic creation

Author: jordibeen

lua/gp/config.lua

@@ -171,6 +171,16 @@ local config = {
 			-- system prompt (use this to specify the persona/role of the AI)
 			system_prompt = require("gp.defaults").chat_system_prompt,
 		},
+		{
+			provider = "anthropic",
+			name = "ChatClaude-Sonnet-4-Thinking",
+			chat = true,
+			command = false,
+			-- string with model name or table with model name and parameters
+			model = { model = "claude-sonnet-4-20250514", thinking_budget = 1024 },
+			-- system prompt (use this to specify the persona/role of the AI)
+			system_prompt = require("gp.defaults").chat_system_prompt,
+		},
 		{
 			provider = "anthropic",
 			name = "ChatClaude-3-5-Haiku",

lua/gp/dispatcher.lua

@@ -158,6 +158,14 @@ D.prepare_payload = function(messages, model, provider)
 			temperature = model.temperature and math.max(0, math.min(2, model.temperature)) or nil,
 			top_p = model.top_p and math.max(0, math.min(1, model.top_p)) or nil,
 		}
+
+		if model.thinking_budget ~= nil then
+			payload.thinking = {
+				type = "enabled",
+				budget_tokens = model.thinking_budget
+			}
+		end
+
 		return payload
 	end
 
@@ -230,6 +238,7 @@ local query = function(buf, provider, payload, handler, on_exit, callback)
 
 	local out_reader = function()
 		local buffer = ""
+		local anthropic_thinking = false -- local state for Anthropic thinking blocks
 
 		---@param lines_chunk string
 		local function process_lines(lines_chunk)
@@ -252,14 +261,24 @@ local query = function(buf, provider, payload, handler, on_exit, callback)
 					end
 				end
 
-				if qt.provider == "anthropic" and line:match('"text":') then
+				if qt.provider == "anthropic" and (line:match('"text":') or line:match('"thinking"')) then
 					if line:match("content_block_start") or line:match("content_block_delta") then
 						line = vim.json.decode(line)
-						if line.delta and line.delta.text then
-							content = line.delta.text
+						if line.content_block then
+							if line.content_block.type == "thinking" then
+								anthropic_thinking = true
+								content = "<think>"
+							elseif line.content_block.type == "text" and anthropic_thinking then
+								anthropic_thinking = false
+								content = "</think>\n\n"
+							end
 						end
-						if line.content_block and line.content_block.text then
-							content = line.content_block.text
+						if line.delta then
+							if line.delta.type == "thinking_delta" then
+								content = line.delta.thinking or ""
+							elseif line.delta.type == "text_delta" then
+								content = line.delta.text or ""
+							end
 						end
 					end
 				end
@@ -382,8 +401,6 @@ local query = function(buf, provider, payload, handler, on_exit, callback)
 			"x-api-key: " .. bearer,
 			"-H",
 			"anthropic-version: 2023-06-01",
-			"-H",
-			"anthropic-beta: messages-2023-12-15",
 		}
 	elseif provider == "azure" then
 		headers = {

lua/gp/init.lua

@@ -1159,11 +1159,17 @@ M.chat_respond = function(params)
 				local topic_buf = vim.api.nvim_create_buf(false, true)
 				local topic_handler = M.dispatcher.create_handler(topic_buf, nil, 0, false, "", false)
 
-				-- call the model
+				-- call the model (remove thinking_budget for Anthropic topic generation)
+				local topic_model = headers.model or agent.model
+				local provider = headers.provider or agent.provider
+				if provider == "anthropic" and topic_model.thinking_budget then
+					topic_model = vim.deepcopy(topic_model)
+					topic_model.thinking_budget = nil
+				end
 				M.dispatcher.query(
 					nil,
-					headers.provider or agent.provider,
-					M.dispatcher.prepare_payload(messages, headers.model or agent.model, headers.provider or agent.provider),
+					provider,
+					M.dispatcher.prepare_payload(messages, topic_model, provider),
 					topic_handler,
 					vim.schedule_wrap(function()
 						-- get topic from invisible buffer