DeepSeek V4.1 Flash in DeepSeek Harness

DeepSeek V4.1 Flash in Harness: Setup & Model ID

Q: Which model ID should DSH send for V4.1 Flash?

Use deepseek-flash. The missing dot in one current DSH display label does not change the API model ID.

Q: Which reasoning effort should I choose?

Start with high for normal coding and Agent work. Use max when the task justifies additional inference cost, and compare outcomes rather than assuming the benchmark setting is always best.

Author: DeepSeekAgent.io Editorial Team
Published: Sep 11, 2026
Updated: Sep 11, 2026

DeepSeek V4.1 Flash is available through the official DeepSeek API as deepseek-flash. The current @deepseek-ai/dsh-llm-deepseek source also includes this ID in its default model catalog, declares text and image input, uses a one-million-token context default, and supports off, low, high, and max reasoning settings.

This guide focuses on the boundary between the model and the Harness: which ID to select, what DSH sends, how image capability is declared, and what to verify when migrating an existing V4 Flash session.

Use the current model ID

For a new official-API configuration, select:

deepseek-flash

DeepSeek says the retired deepseek-v4-flash and deepseek-v4-flash-vision-exp IDs temporarily route to V4.1 Flash. Those aliases reduce immediate breakage, but they are compatibility paths. A new profile should use deepseek-flash so its target is explicit.

The current DSH catalog may display DeepSeek-V41-Flash without the dot after V4. Its underlying ID is still deepseek-flash. A community discussion identified this as a display-label issue in @deepseek-ai/[email protected]; the repository source confirms the ID and the label. Do not change the request model to match the typo.

Start with the built-in official route

When DSH uses the official DeepSeek provider and its default model catalog, the current source supplies the V4.1 entry automatically. Keep the API key in the environment rather than writing the secret into a Composition file:

export DEEPSEEK_API_KEY="your-key"

Then choose deepseek-flash in the DSH model selector or Profile. If your installed package predates the V4.1 catalog entry, upgrade through the package channel you intentionally use or add an explicit catalog entry after backing up the configuration.

Custom compatible endpoint example

The following structure is useful when a compatible gateway exposes V4.1 Flash. Match the base URL and limits to that provider:

- name: '@deepseek-ai/dsh-llm-deepseek'
  config:
    apiKeyEnv: DEEPSEEK_API_KEY
    baseURL: https://your-compatible-endpoint.example/v1
    reasoningEffort: high
    maxTokens: 256000
    defaultContextWindow: 1000000
    models:
      - id: deepseek-flash
        name: DeepSeek-V4.1-Flash
        inputModalities:
          - text
          - image
        contextWindow: 1000000
        maxTokens: 256000

An explicit models array replaces the default catalog. Copy every other entry you still need. Also verify that the gateway really accepts the official model ID; compatible services sometimes publish their own deployment names.

Reasoning effort and output limits

The model supports a continuous 1–100 reasoning scale at the API level. The current DSH plugin exposes four user-facing choices: off, low, high, and max, with high as the plugin default. DeepSeek's published instruct benchmark uses maximum effort, so those results should not be treated as expected performance at high or low.

Use high as a practical starting point for everyday coding. Reserve max for difficult debugging, repository-scale planning, or benchmark reproduction, then measure quality and cost on your own tasks. The official model card recommends an output allowance of at least 256K for its evaluation-oriented setup; a smaller production cap may be appropriate when your tasks are bounded.

Image input checks

The official model is natively multimodal. In the current DSH catalog, deepseek-flash declares both text and image. For a custom catalog, preserve that declaration or the Session controller can reject an attachment before the request reaches the model.

When an image fails:

Confirm the selected entry is deepseek-flash.
Check that inputModalities contains text and image.
Send a small JPEG or PNG before testing a large screenshot set.
Verify the compatible endpoint supports V4.1 image input and the same transport format.
Separate a DSH capability error from an upstream API error.

See the DSH vision-model troubleshooting guide for the full attachment path.

Migration checklist from V4 Flash

Change new configurations to deepseek-flash.
Keep the old ID only while you deliberately rely on the temporary alias.
Start a fresh smoke-test Session before continuing an important historical trajectory.
Test one text task, one image task, and one real tool-using task.
Record DSH version, Profile, reasoning effort, endpoint, model ID, runtime, token accounting, and outcome.
Recheck custom model lists because they replace the defaults.

Long context is capacity, not a promise that every session should grow to one million tokens. A community report describes a reasoning loop in one very long, maximum-effort run. That report is useful as a troubleshooting signal, but it does not establish a general V4.1 defect. If a session stops producing useful tool or text events, save the trajectory, retry from a clean checkpoint, lower the effort, and compare against a shorter context.

FAQ

Which model ID should DSH send for V4.1 Flash?

Use deepseek-flash. The missing dot in one current DSH display label does not change the API model ID.

Should I keep using deepseek-v4-flash?

DeepSeek currently routes that retired ID to V4.1 Flash for compatibility. New configurations should use deepseek-flash because the alias is temporary.

Which reasoning effort should I choose?

Start with high for normal coding and Agent work. Use max when the task justifies additional inference cost, and compare outcomes rather than assuming the benchmark setting is always best.