FULL STORY
Gemini 4 Pro: From Anonymous Arena Runs to Leaked Demos
An anonymous "Gemini 3.8 Flash" spotted on LMArena was widely believed to be Google's unreleased Gemini 4 Pro, followed by leaked demo videos and outputs showing impressive generative performance.
2026-09-17 ~ 2026-09-19 · 2 episodes · 15 posts
Episode 1 · Suspected Gemini 4 Pro quietly testing on LMArena under "3.8 Flash" alias (2026-09-17, 13 posts)
On September 17, several AI benchmarking accounts spotted an anonymous model coded "Gemini 3.8 Flash" on LMArena, speculating it is actually a checkpoint of Google's upcoming Gemini 4 Pro (or 4.0 Pro) undergoing pre-release blind testing under a disguised name. Google has not confirmed anything.
Confirmed
- Anonymous test entries appeared on the Arena leaderboard, showing battle links for "Gemini 3.8 Flash (high)" against "Gemini 4".
- Community users ran comparison tests against the existing Gemini 3.8 Flash.
- One user tested it with the "pelican riding a bicycle SVG" prompt, and the model performed impressively.
Not yet confirmed
- Whether the anonymous model is truly Gemini 4 Pro remains community speculation; Google has not verified it.
- After hands-on testing, @cedricchee judged its 3D capabilities to fall well short of earlier versions of 4 Pro—close to the leap seen from the Sol-to-Astra generation—though he gave this only about 75% confidence.
Why it matters
- Models appearing on LMArena under disguised codenames typically signal official blind testing ahead of a formal release, often hinting a launch is near.
- @teortaxesTex quipped that if the anonymous model really is Gemini 4 Pro, Arena's current test prompts (such as SVG generation) are too easy to fully gauge a flagship model's true capabilities.
- If the identity holds, this would provide the first directly comparable data point between Gemini 4 Pro and the existing 3.8 Flash.
- 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
- gemini-3.8-flash appears on LMArena, 'Gemini 4 Pro' leak sparks unconfirmed rumors — gaganghotra_ · 2026-09-18
- 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
- Rumor: Gemini 4 Pro Testing Anonymously in LM Arena as "Gemini 3.8 Flash" — koltregaskes · 2026-09-18
Episode 2 · Alleged Gemini 4 Pro Demos Leak, Impressive Output Reported (2026-09-18, 2 posts)
Unverified demos and an alleged first output of Gemini 4 Pro have leaked, including a smooth game-generation demo praised for its world generation, fueling expectations that Google is regaining its form.
- Leaked Gemini 4 Pro first output shows polished game generation, unverified — CodeByPoonam · 2026-09-18
- Unposted demo videos of Gemini 4 Pro reportedly look impressive — ChrisGPT · 2026-09-19