Suspected Gemini 4 Pro Surfaces Anonymously on LMArena as '3.8 Flash'
Since September 17, multiple AI-testing accounts discovered an anonymous model labeled "Gemini 3.8 Flash" on LMArena, widely believed to be a pre-release checkpoint of Google's upcoming Gemini 4 Pro undergoing blind testing under a disguised name. Hands-on feedback the next day described it as fast and cheap, far above typical Flash-tier performance on agent and coding tasks, and side-by-side comparisons showed better output quality than the existing 3.8 Flash. Google has not confirmed anything; all conclusions come from community leaks and informal tests.
Confirmed
- Anonymous test entries appeared on the Arena leaderboard: @cedricchee noted cited links showing battles between "Gemini 3.8 Flash (high)" and "Gemini 4"; @koltregaskes relayed the same via a leak from @aiforsuccess.
- Users compared it against the existing Gemini 3.8 Flash: @CodeByPoonam compiled 10 user-generated wild examples on September 18, covering SVG animations and Three.js scenes; same-prompt side-by-side comparisons showed the routed-to new Pro model producing better output.
- @CodeByPoonam shared one-line-prompt demos: a Three.js rocket scene, a cloud-whale SVG deemed more polished than the previous checkpoint, and a cycling-peacock animated SVG with surprisingly good animation.
- @gaganghotra added on September 18 that the model is fast and cheap, exceeding Flash-tier expectations on agent and coding tasks, alongside screenshots hinting "Gemini 4 Pro" had entered the Arena.
Unconfirmed
- Whether the model truly is Gemini 4 Pro remains community speculation; Google has not verified it.
- @cedricchee judged its 3D capability a leap comparable to the Sol-to-Astra generation jump versus prior 4 Pro versions, but with only 75% personal confidence.
- Some users worry Google could nerf this checkpoint before launch; this is emotional speculation.
Why it matters
- Disguised checkpoints on LMArena typically signal blind testing shortly before an official release.
- @teortaxesTex quipped that if it really is Gemini 4 Pro, current Arena prompts (like SVG generation) are too easy to gauge a flagship's true level.
- If confirmed, this provides a direct comparable data point between Gemini 4 Pro and the existing 3.8 Flash, and the "fast and cheap" feedback hints its pricing and performance positioning may diverge sharply from the traditional Flash line.
2026-09-17 ~ 2026-09-18 · 13 related posts
- Episode 1: Suspected Gemini 4 Pro Surfaces Anonymously on LMArena as '3.8 Flash'(2026-09-17, 13 posts)
- Episode 2: Alleged Gemini 4 Pro Demos Leak, Impressive Output Reported(2026-09-18, 2 posts)
- Episode 3: Mysterious "Gemini 3.8 Flash" appears on LMArena(2026-09-28, 3 posts)
Primary sources
- [source] Gemini 4 Pro Checkpoint Spotted in LMArena Amid Codename Leak — cedric_chee · 2026-09-17
- Gemini 4 Pro checkpoint spotted testing in LMArena under the name 'Gemini 3.8 flash' — airesearch12 · 2026-09-17
- Rumor: Gemini 4.0 Pro spotted testing in LMArena under the name Gemini 3.8 Flash — gaganghotra_ · 2026-09-17
- Suspected Gemini 4 Pro spotted in Arena as gemini-3.8-flash; critics want harder tests — teortaxesTex · 2026-09-17
- Gemini 4 Pro checkpoint spotted in Arena, 3D gains rival Sol-to-Astra jump — cedric_chee · 2026-09-17
- Gemini 4 Pro Checkpoint Spotted in LMArena — cedric_chee · 2026-09-17
- [source] gemini-3.8-flash appears on LMArena, 'Gemini 4 Pro' leak sparks unconfirmed rumors — gaganghotra_ · 2026-09-18
- [source] Rumored Gemini 4 checkpoint spotted in LMArena as users share 10 demo outputs — CodeByPoonam · 2026-09-18
- Side-by-side: suspected Gemini 4 Pro vs Gemini 3.8 Flash in LMArena — CodeByPoonam · 2026-09-18
- Suspected Gemini 4 Pro renders a polished flying-whale SVG, users say quality jumped — CodeByPoonam · 2026-09-18
- Suspected Gemini 4 Pro builds a Three.js rocket from a single-line prompt — CodeByPoonam · 2026-09-18
- Suspected Gemini 4 Pro generates animated peacock-on-a-bike SVG in Arena — CodeByPoonam · 2026-09-18
1 near-duplicate retellings: koltregaskes