CURRENT MODEL COMPARISON / 2026

GPT-6 Luna vs Gemini 3.8 Flash

Which September 2026 edition fits a structured, high-volume application?

Reviewed Live model evidence ↗
OpenAI

GPT-6 Luna↗

A September 2026 reasoning model with text and image inputs and text output.

Access type
Hosted API
Original release date
Model ID
gpt-6-luna
Input / output
Text and image inputs; text output
API formats
Responses and Chat Completions; Decisions beta added October 6, 2026
License / terms
Provider service terms

Responses and Chat Completions are supported; the Decisions API was added in beta on October 6, 2026. Evaluate that endpoint separately and recheck prices and token tiers.

Official source ↗Latest artifacts and release journal →
Google

Gemini 3.8 Flash↗

A September 2026 generally available Gemini release for software engineering, agents and enterprise workflows.

Access type
Hosted API
Original release date
Model ID
gemini-3.8-flash
Source focus
Software engineering, autonomous agents and enterprise workflows
License / terms
Provider service terms

The provider announcement describes intended uses, not an independent result in your application. Check accepted inputs, thinking controls and current pricing on the selected Gemini endpoint.

Official source ↗Latest artifacts and release journal →

The decision to test

Use a fixed dataset and a separate difficult subset. Luna launched September 22, 2026, and Gemini 3.8 Flash reached general availability September 2. Match the application behavior while keeping native endpoint differences documented.

Treat endpoint choice as part of the experiment

Luna can be evaluated through Responses or Chat Completions; Decisions became a separate beta option October 6. Gemini uses its own request and thinking controls. Save the chosen endpoint and configuration with every result.

Include repair in the outcome

Record invalid structures, wrong values, missing fields and retries separately. Then calculate spend per correct accepted result. A fast schema-compliant answer can still create expensive manual work.

Three criteria for this comparison

  1. Labeled decision and extraction accuracy
  2. Actual endpoint and thinking configuration
  3. Accepted-result cost under realistic load

Run a fair comparison

Use the same representative inputs and a written answer rubric. Pin the model version and record the endpoint, thinking configuration, quantization when known, context length, output allowance and concurrency. Preserve native request differences in an adapter rather than silently dropping fields.

Measure full request time, error rate and reported usage. For tools, validate arguments and score the result after execution. For images, preserve resolution and preprocessing. A valid response format alone does not establish a correct answer.

Compare cost per accepted result

Calculate input cost plus all billed output, including reasoning where the provider counts it. Add retries and discarded answers. Divide the total by the number of results that pass your quality criteria. Keep API usage cost separate from deployment and engineering cost.

Estimate token costs with the API calculator →

Independent benchmark evidence

Open the full live comparison →
Latest recorded measurements aligned by exact artifact, benchmark version, source and methodology. These are source results, not tests of Flonno's deployment.
Benchmark / sourceGPT-6 LunaGemini 3.8 Flash
Artificial Analysis Intelligence Indexv4.3 · Artificial Analysis38.1 index_pointsMeasured Oct 1, 2026Original result ↗40.9 index_pointsMeasured Sep 20, 2026Original result ↗

Artificial Analysis observations are refreshed by the integrated Radar. Differences in artifact, benchmark version or method prevent a score comparison. Read the evidence methodology →

YOUR WORKLOAD

Compare cost per accepted task.

Enter results from your own evaluation. A task should count once it meets your written quality criteria. Include failed attempts and retries in total spend. These inputs stay in this browser and are not a Flonno benchmark.

GPT-6 Luna
Gemini 3.8 Flash
GPT-6 Luna

Enter all four values. Attempted tasks must be at least one; accepted tasks cannot exceed attempted tasks.

Gemini 3.8 Flash

Enter all four values. Attempted tasks must be at least one; accepted tasks cannot exceed attempted tasks.

Turn evidence into a deployment decision

A source benchmark can inform your shortlist, while your evaluation shows whether a model finishes the work at an acceptable cost. Keep the chosen endpoint, processing terms and output limits in the decision record. Inclusion in the Radar does not mean the model is served by Flonno.

For the API currently offered here, explore Qwen3.8 Flash 27B and the production evaluation guide.

Release coverage and updates

Model journal →

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Browse current guides →