diff --git a/CHANGELOG.md b/CHANGELOG.md
index 46c363645..8f461e1f7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+- Fixed MCP `ask_codebase` rejecting explicit language model selection by resolving matching model configurations when `displayName` is omitted and providing clear disambiguation errors for multi-config models. [#1622](https://github.com/sourcebot-dev/sourcebot/pull/1622)
+
 ## [5.1.10] - 2026-08-27
 
 ### Fixed
diff --git a/packages/web/src/ee/features/mcp/askCodebase.ts b/packages/web/src/ee/features/mcp/askCodebase.ts
index 35337d29f..4bf681203 100644
--- a/packages/web/src/ee/features/mcp/askCodebase.ts
+++ b/packages/web/src/ee/features/mcp/askCodebase.ts
@@ -4,7 +4,8 @@ import { generateChatNameFromMessage } from "@/ee/features/chat/llm.server";
 import { getAISDKLanguageModelAndOptions } from "@/features/chat/llm.server";
 import { resolveContextWindow } from "@/features/chat/modelContextWindow.server";
 import { LanguageModelInfo, SBChatMessage, SearchScope } from "@/features/chat/types";
-import { convertLLMOutputToPortableMarkdown, getAnswerPartFromAssistantMessage, getLanguageModelKey } from "@/features/chat/utils";
+import { convertLLMOutputToPortableMarkdown, getAnswerPartFromAssistantMessage } from "@/features/chat/utils";
+import { selectConfiguredLanguageModel } from "@/features/chat/selectConfiguredLanguageModel";
 import { resolveModelCapabilities } from "@/features/chat/modelCapabilities.server";
 import { ErrorCode } from "@/lib/errorCodes";
 import { ServiceError, ServiceErrorException } from "@/lib/serviceError";
@@ -61,28 +62,11 @@ export const askCodebase = (params: AskCodebaseParams): Promise<AskCodebaseResul
             const { query, repos = [], languageModel: requestedLanguageModel, visibility: requestedVisibility, source } = params;
 
             const configuredModels = await getConfiguredLanguageModels();
-            if (configuredModels.length === 0) {
-                return {
-                    statusCode: StatusCodes.BAD_REQUEST,
-                    errorCode: ErrorCode.INVALID_REQUEST_BODY,
-                    message: "No language models are configured. Please configure at least one language model. See: https://docs.sourcebot.dev/docs/configuration/language-model-providers",
-                } satisfies ServiceError;
-            }
-
-            let languageModelConfig = configuredModels[0];
-            if (requestedLanguageModel) {
-                const matchingModel = configuredModels.find(
-                    (m) => getLanguageModelKey(m) === getLanguageModelKey(requestedLanguageModel)
-                );
-                if (!matchingModel) {
-                    return {
-                        statusCode: StatusCodes.BAD_REQUEST,
-                        errorCode: ErrorCode.INVALID_REQUEST_BODY,
-                        message: `Language model '${requestedLanguageModel.provider}/${requestedLanguageModel.model}' is not configured.`,
-                    } satisfies ServiceError;
-                }
-                languageModelConfig = matchingModel;
+            const modelSelection = selectConfiguredLanguageModel(configuredModels, requestedLanguageModel);
+            if (!modelSelection.success) {
+                return modelSelection.error;
             }
+            const languageModelConfig = modelSelection.model;
 
             const { model, providerOptions, temperature } = await getAISDKLanguageModelAndOptions(languageModelConfig);
             const modelName = languageModelConfig.displayName ?? languageModelConfig.model;
diff --git a/packages/web/src/features/chat/selectConfiguredLanguageModel.test.ts b/packages/web/src/features/chat/selectConfiguredLanguageModel.test.ts
new file mode 100644
index 000000000..cde15754c
--- /dev/null
+++ b/packages/web/src/features/chat/selectConfiguredLanguageModel.test.ts
@@ -0,0 +1,182 @@
+import { describe, expect, test } from "vitest";
+import { selectConfiguredLanguageModel } from "./selectConfiguredLanguageModel";
+import { StatusCodes } from "http-status-codes";
+import { ErrorCode } from "@/lib/errorCodes";
+
+describe("selectConfiguredLanguageModel", () => {
+    const model1 = {
+        provider: "anthropic",
+        model: "claude-sonnet-4-6",
+        displayName: "Claude Sonnet 4.6",
+    };
+
+    const model2 = {
+        provider: "anthropic",
+        model: "claude-opus-4-7",
+        displayName: "Claude Opus 4.7 (Fast)",
+    };
+
+    const model3 = {
+        provider: "anthropic",
+        model: "claude-opus-4-7",
+        displayName: "Claude Opus 4.7 (Thinking)",
+    };
+
+    const model4 = {
+        provider: "openai",
+        model: "gpt-4o",
+    };
+
+    const configuredModels = [model1, model2, model3, model4];
+
+    test("returns error when no models are configured", () => {
+        const result = selectConfiguredLanguageModel([], {
+            provider: "anthropic",
+            model: "claude-sonnet-4-6",
+        });
+
+        expect(result.success).toBe(false);
+        if (!result.success) {
+            expect(result.error.statusCode).toBe(StatusCodes.BAD_REQUEST);
+            expect(result.error.errorCode).toBe(ErrorCode.INVALID_REQUEST_BODY);
+            expect(result.error.message).toContain("No language models are configured");
+        }
+    });
+
+    test("defaults to first configured model when no requested model is provided", () => {
+        const result = selectConfiguredLanguageModel(configuredModels);
+
+        expect(result.success).toBe(true);
+        if (result.success) {
+            expect(result.model).toEqual(model1);
+        }
+    });
+
+    test("defaults to first configured model when empty object is provided", () => {
+        const result = selectConfiguredLanguageModel(configuredModels, {});
+
+        expect(result.success).toBe(true);
+        if (result.success) {
+            expect(result.model).toEqual(model1);
+        }
+    });
+
+    test("matches model uniquely by provider and model when displayName is omitted", () => {
+        const result = selectConfiguredLanguageModel(configuredModels, {
+            provider: "anthropic",
+            model: "claude-sonnet-4-6",
+        });
+
+        expect(result.success).toBe(true);
+        if (result.success) {
+            expect(result.model).toEqual(model1);
+        }
+    });
+
+    test("matches model uniquely when configured model has no displayName and request omits it", () => {
+        const result = selectConfiguredLanguageModel(configuredModels, {
+            provider: "openai",
+            model: "gpt-4o",
+        });
+
+        expect(result.success).toBe(true);
+        if (result.success) {
+            expect(result.model).toEqual(model4);
+        }
+    });
+
+    test("matches model strictly by exact provider, model, and displayName", () => {
+        const result = selectConfiguredLanguageModel(configuredModels, {
+            provider: "anthropic",
+            model: "claude-opus-4-7",
+            displayName: "Claude Opus 4.7 (Thinking)",
+        });
+
+        expect(result.success).toBe(true);
+        if (result.success) {
+            expect(result.model).toEqual(model3);
+        }
+    });
+
+    test("returns 400 with disambiguation message when multiple models match provider/model and displayName is omitted", () => {
+        const result = selectConfiguredLanguageModel(configuredModels, {
+            provider: "anthropic",
+            model: "claude-opus-4-7",
+        });
+
+        expect(result.success).toBe(false);
+        if (!result.success) {
+            expect(result.error.statusCode).toBe(StatusCodes.BAD_REQUEST);
+            expect(result.error.errorCode).toBe(ErrorCode.INVALID_REQUEST_BODY);
+            expect(result.error.message).toContain("Multiple configurations found for language model 'anthropic/claude-opus-4-7'");
+            expect(result.error.message).toContain("'Claude Opus 4.7 (Fast)'");
+            expect(result.error.message).toContain("'Claude Opus 4.7 (Thinking)'");
+            expect(result.error.message).not.toContain("(default)");
+        }
+    });
+
+    test("handles multiple models with identical provider/model when none have displayName", () => {
+        const duplicateUnnamed = [
+            { provider: "ollama", model: "llama3" },
+            { provider: "ollama", model: "llama3" },
+        ];
+
+        const result = selectConfiguredLanguageModel(duplicateUnnamed, {
+            provider: "ollama",
+            model: "llama3",
+        });
+
+        expect(result.success).toBe(false);
+        if (!result.success) {
+            expect(result.error.statusCode).toBe(StatusCodes.BAD_REQUEST);
+            expect(result.error.errorCode).toBe(ErrorCode.INVALID_REQUEST_BODY);
+            expect(result.error.message).toContain("Please configure distinct displayNames in your configuration");
+        }
+    });
+
+    test("returns 400 when model is not configured", () => {
+        const result = selectConfiguredLanguageModel(configuredModels, {
+            provider: "google",
+            model: "gemini-2.0-flash",
+        });
+
+        expect(result.success).toBe(false);
+        if (!result.success) {
+            expect(result.error.statusCode).toBe(StatusCodes.BAD_REQUEST);
+            expect(result.error.errorCode).toBe(ErrorCode.INVALID_REQUEST_BODY);
+            expect(result.error.message).toBe("Language model 'google/gemini-2.0-flash' is not configured.");
+        }
+    });
+
+    test("returns 400 when provider/model matches but displayName does not match any config", () => {
+        const result = selectConfiguredLanguageModel(configuredModels, {
+            provider: "anthropic",
+            model: "claude-sonnet-4-6",
+            displayName: "Nonexistent Display Name",
+        });
+
+        expect(result.success).toBe(false);
+        if (!result.success) {
+            expect(result.error.statusCode).toBe(StatusCodes.BAD_REQUEST);
+            expect(result.error.errorCode).toBe(ErrorCode.INVALID_REQUEST_BODY);
+            expect(result.error.message).toBe("Language model 'anthropic/claude-sonnet-4-6' ('Nonexistent Display Name') is not configured.");
+        }
+    });
+
+    test("matches when displayName is empty string if configured with empty string", () => {
+        const modelsWithEmpty = [
+            { provider: "openai", model: "gpt-4o", displayName: "" },
+        ];
+
+        const result = selectConfiguredLanguageModel(modelsWithEmpty, {
+            provider: "openai",
+            model: "gpt-4o",
+            displayName: "",
+        });
+
+        expect(result.success).toBe(true);
+        if (result.success) {
+            expect(result.model.displayName).toBe("");
+        }
+    });
+});
diff --git a/packages/web/src/features/chat/selectConfiguredLanguageModel.ts b/packages/web/src/features/chat/selectConfiguredLanguageModel.ts
new file mode 100644
index 000000000..bbe96f442
--- /dev/null
+++ b/packages/web/src/features/chat/selectConfiguredLanguageModel.ts
@@ -0,0 +1,100 @@
+import { StatusCodes } from "http-status-codes";
+import { ErrorCode } from "@/lib/errorCodes";
+import { ServiceError } from "@/lib/serviceError";
+
+export type SelectConfiguredLanguageModelResult<T> =
+    | { success: true; model: T }
+    | { success: false; error: ServiceError };
+
+type MatchableModel = {
+    provider: string;
+    model: string;
+    displayName?: string;
+};
+
+export const selectConfiguredLanguageModel = <T extends MatchableModel>(
+    configuredModels: T[],
+    requestedLanguageModel?: Partial<MatchableModel>
+): SelectConfiguredLanguageModelResult<T> => {
+    if (configuredModels.length === 0) {
+        return {
+            success: false,
+            error: {
+                statusCode: StatusCodes.BAD_REQUEST,
+                errorCode: ErrorCode.INVALID_REQUEST_BODY,
+                message: "No language models are configured. Please configure at least one language model. See: https://docs.sourcebot.dev/docs/configuration/language-model-providers",
+            },
+        };
+    }
+
+    if (!requestedLanguageModel || (!requestedLanguageModel.provider && !requestedLanguageModel.model)) {
+        return {
+            success: true,
+            model: configuredModels[0],
+        };
+    }
+
+    const { provider, model, displayName } = requestedLanguageModel;
+
+    if (displayName !== undefined) {
+        const exactMatch = configuredModels.find((m) => {
+            return m.provider === provider && m.model === model && m.displayName === displayName;
+        });
+
+        if (exactMatch) {
+            return {
+                success: true,
+                model: exactMatch,
+            };
+        }
+
+        return {
+            success: false,
+            error: {
+                statusCode: StatusCodes.BAD_REQUEST,
+                errorCode: ErrorCode.INVALID_REQUEST_BODY,
+                message: `Language model '${provider}/${model}' ('${displayName}') is not configured.`,
+            },
+        };
+    }
+
+    const matchingModels = configuredModels.filter((m) => {
+        return m.provider === provider && m.model === model;
+    });
+
+    if (matchingModels.length === 1) {
+        return {
+            success: true,
+            model: matchingModels[0],
+        };
+    }
+
+    if (matchingModels.length > 1) {
+        const availableNames = matchingModels
+            .map((m) => m.displayName)
+            .filter((name): name is string => typeof name === "string" && name.length > 0)
+            .map((name) => `'${name}'`);
+
+        const hint = availableNames.length > 0
+            ? `Please specify a displayName (${availableNames.join(', ')}) to disambiguate.`
+            : `Please configure distinct displayNames in your configuration to disambiguate.`;
+
+        return {
+            success: false,
+            error: {
+                statusCode: StatusCodes.BAD_REQUEST,
+                errorCode: ErrorCode.INVALID_REQUEST_BODY,
+                message: `Multiple configurations found for language model '${provider}/${model}'. ${hint}`,
+            },
+        };
+    }
+
+    return {
+        success: false,
+        error: {
+            statusCode: StatusCodes.BAD_REQUEST,
+            errorCode: ErrorCode.INVALID_REQUEST_BODY,
+            message: `Language model '${provider}/${model}' is not configured.`,
+        },
+    };
+};