diff --git a/internal/services/toolkit/client/client_v2.go b/internal/services/toolkit/client/client_v2.go
index 8279b6bc..eb83f793 100644
--- a/internal/services/toolkit/client/client_v2.go
+++ b/internal/services/toolkit/client/client_v2.go
@@ -63,11 +63,30 @@ func NewAIClientV2(
 	logger *logger.Logger,
 ) *AIClientV2 {
 	database := db.Database("paperdebugger")
+
+	llmProvider := &models.LLMProviderConfig{
+		APIKey: cfg.OpenAIAPIKey,
+	}
+
+	var baseUrl string
+	var apiKey string
+	var modelSlug string
+
+	if llmProvider != nil && llmProvider.IsCustom() {
+		baseUrl = cfg.OpenAIBaseURL
+		apiKey = cfg.OpenAIAPIKey
+		modelSlug = "gpt-5-nano"
+	} else {
+		baseUrl = cfg.InferenceBaseURL + "/openrouter"
+		apiKey = cfg.InferenceAPIKey
+		modelSlug = "openai/gpt-5-nano"
+	}
+
 	oaiClient := openai.NewClient(
-		option.WithBaseURL(cfg.InferenceBaseURL+"/openrouter"),
-		option.WithAPIKey(cfg.InferenceAPIKey),
+		option.WithBaseURL(baseUrl),
+		option.WithAPIKey(apiKey),
 	)
-	CheckOpenAIWorksV2(oaiClient, logger)
+	CheckOpenAIWorksV2(oaiClient, baseUrl, modelSlug, logger)
 
 	toolRegistry := initializeToolkitV2(db, projectService, cfg, logger)
 	toolCallHandler := handler.NewToolCallHandlerV2(toolRegistry)
diff --git a/internal/services/toolkit/client/completion_v2.go b/internal/services/toolkit/client/completion_v2.go
index e7e5b7b2..a428edc6 100644
--- a/internal/services/toolkit/client/completion_v2.go
+++ b/internal/services/toolkit/client/completion_v2.go
@@ -65,7 +65,8 @@ func (a *AIClientV2) ChatCompletionStreamV2(ctx context.Context, callbackStream
 	}()
 
 	oaiClient := a.GetOpenAIClient(llmProvider)
-	params := getDefaultParamsV2(modelSlug, a.toolCallHandler.Registry)
+	var isCustomModel bool = llmProvider != nil && llmProvider.IsCustom()
+	params := getDefaultParamsV2(modelSlug, a.toolCallHandler.Registry, isCustomModel)
 
 	for {
 		params.Messages = openaiChatHistory
diff --git a/internal/services/toolkit/client/utils_v2.go b/internal/services/toolkit/client/utils_v2.go
index e502cb21..2fa04b94 100644
--- a/internal/services/toolkit/client/utils_v2.go
+++ b/internal/services/toolkit/client/utils_v2.go
@@ -6,6 +6,7 @@ This file contains utility functions for the client package. (Mainly miscellaneo
 It is used to append assistant responses to both OpenAI and in-app chat histories, and to create response items for chat interactions.
 */
 import (
+	"path"
 	"context"
 	"fmt"
 	"paperdebugger/internal/libs/cfg"
@@ -15,7 +16,6 @@ import (
 	"paperdebugger/internal/services/toolkit/registry"
 	"paperdebugger/internal/services/toolkit/tools/xtramcp"
 	chatv2 "paperdebugger/pkg/gen/api/chat/v2"
-	"strings"
 	"time"
 
 	openaiv3 "github.com/openai/openai-go/v3"
@@ -52,7 +52,12 @@ func appendAssistantTextResponseV2(openaiChatHistory *OpenAIChatHistory, inappCh
 	})
 }
 
-func getDefaultParamsV2(modelSlug string, toolRegistry *registry.ToolRegistryV2) openaiv3.ChatCompletionNewParams {
+func getDefaultParamsV2(modelSlug string, toolRegistry *registry.ToolRegistryV2, isCustomModel bool) openaiv3.ChatCompletionNewParams {
+	// If custom model is used, strip prefix (eg "openai/gpt-4o" -> "gpt-4o")
+	if isCustomModel {
+		modelSlug = path.Base(modelSlug)
+	}
+
 	var reasoningModels = []string{
 		"gpt-5",
 		"gpt-5-mini",
@@ -66,7 +71,7 @@ func getDefaultParamsV2(modelSlug string, toolRegistry *registry.ToolRegistryV2)
 		"codex-mini-latest",
 	}
 	for _, model := range reasoningModels {
-		if strings.Contains(modelSlug, model) {
+		if modelSlug == model {
 			return openaiv3.ChatCompletionNewParams{
 				Model:               modelSlug,
 				MaxCompletionTokens: openaiv3.Int(4000),
@@ -87,13 +92,13 @@ func getDefaultParamsV2(modelSlug string, toolRegistry *registry.ToolRegistryV2)
 	}
 }
 
-func CheckOpenAIWorksV2(oaiClient openaiv3.Client, logger *logger.Logger) {
-	logger.Info("[AI Client V2] checking if openai client works")
+func CheckOpenAIWorksV2(oaiClient openaiv3.Client, baseUrl string, model string, logger *logger.Logger) {
+	logger.Info("[AI Client V2] checking if openai client works with " + baseUrl + "..")
 	chatCompletion, err := oaiClient.Chat.Completions.New(context.TODO(), openaiv3.ChatCompletionNewParams{
 		Messages: []openaiv3.ChatCompletionMessageParamUnion{
 			openaiv3.UserMessage("Say 'openai client works'"),
 		},
-		Model: "openai/gpt-5-nano",
+		Model: model,
 	})
 	if err != nil {
 		logger.Errorf("[AI Client V2] openai client does not work: %v", err)