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lucidity · Efficient

Synth 2.5 Flash Preview

Added Sep 5, 2026

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Use in the app

Synth 2.5 Flash Preview is a low-cost text model designed for role-play, character dialogue, and collaborative storytelling.

Input
Text
Output
Text
Discovery tier
Efficient

Pricing

USD per 1M tokens
Input
$0.03
Output
$0.10

Reference prices as published by the model provider. API example

Specifications

Context window
30K
Max output
—

Side by side

Synth 2.5 Flash Preview compared

Specifications, prices, speed and benchmark scores next to each other. Benchmarks below show every compared model too.

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Synth 2.5 Flash PreviewlucidityThis modelSolar Pro 4upstageRemove
Providerlucidityupstage
Discovery tierEfficientEfficient
AddedSep 5, 2026Aug 11, 2026
Limits
Context window30K524.29KBest
Max output—131.07K
Average output—546 tokens
Pricing, USD per 1M tokens
Input$0.03$0.03
Output$0.10Best$0.12
Cache read—$0.006
Performance
Throughput—100.1 tok/s
Time to first token—3.1 s
Request success (24h)—99.9%
Benchmark indexes
Intelligence Index—26.6
Capabilities
ToolsNoYes
Structured outputNoYes
Reasoning effort——

Public evaluations

Benchmarks

Independent evaluation results, with how each score ranks among the models in the Noumen catalog.

  • Synth 2.5 Flash Preview
  • Solar Pro 4

Intelligence Index

  • Synth 2.5 Flash Preview—
  • Solar Pro 426.6
3.8Catalog models by score55.1

Agentic work

  • AutomationBench-AA

    Workflow automation, penalized for guardrail violations

    • Synth 2.5 Flash Preview: —
    • Solar Pro 4: 13.6%

  • AutomationBench-AA tasks completed

    Workflows finished end to end without a guardrail violation

    • Synth 2.5 Flash Preview: —
    • Solar Pro 4: 2.4%

  • AA-Briefcasev1.1

    Agentic knowledge work, rated head to head

    • Synth 2.5 Flash Preview: —
    • Solar Pro 4: 1,093 Elo

  • GDPval-AAv2.1

    Economically valuable occupational tasks, rated head to head

    • Synth 2.5 Flash Preview: —
    • Solar Pro 4: 1,106 Elo

Document reasoning

  • GDP.pdf

    Professional reasoning over PDF documents, all-pass rate

    • Synth 2.5 Flash Preview: —
    • Solar Pro 4: 7.0%

  • AA-LCRv1.1

    Reasoning across long documents

    • Synth 2.5 Flash Preview: —
    • Solar Pro 4: 70.7%

Reasoning and knowledge

  • Humanity’s Last Exam

    Expert-level questions across academic fields

    • Synth 2.5 Flash Preview: —
    • Solar Pro 4: 29.8%

  • GPQA Diamond

    Graduate-level science questions

    • Synth 2.5 Flash Preview: —
    • Solar Pro 4: 89.1%

Coding

  • Terminal-Benchv4.0

    Practical software engineering in a terminal

    • Synth 2.5 Flash Preview: —
    • Solar Pro 4: 0.0%

  • SciCode

    Scientific computing in Python

    • Synth 2.5 Flash Preview: —
    • Solar Pro 4: 48.0%

Legacy evaluations

  • AA-LCR (unversioned)

    Long-context reasoning, earlier grading

    • Synth 2.5 Flash Preview: —
    • Solar Pro 4: 70.7%

Scores from Artificial Analysis, updated Oct 26, 2026. Artificial Analysis

Developers

Use it through the API

Noumen’s API is OpenAI-compatible: any Chat Completions client works with a base URL and a key.

Read the quickstart
curl https://www.noumen.xyz/api/v1/chat/completions \
  -H "Authorization: Bearer $NOUMEN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "synth-2.5-flash",
    "messages": [{ "role": "user", "content": "Explain this stack trace." }]
  }'
import os
from openai import OpenAI

client = OpenAI(base_url="https://www.noumen.xyz/api/v1", api_key=os.environ["NOUMEN_API_KEY"])
reply = client.chat.completions.create(
    model="synth-2.5-flash",
    messages=[{"role": "user", "content": "Explain this stack trace."}],
)
print(reply.choices[0].message.content)

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