Bartosz Jedrzejewski

Engineering manager @meta MSL. After work - @BattleCastGG and

[Bartosz Jedrzejewski @e4developer]

@Pack_Tacticss Hey- all art is now either official or made on Inkarnate. I also fixed things like flying and dragons optimising for cone :) if you ever want to give it another look 👀

[Bartosz Jedrzejewski @e4developer]

@Pack_Tacticss hey! I see you post really cool tactical content on youtube! Was wondering if you would be intereted in checking out https://t.co/o2CnI5a5Mi (100% free project I created) and if there are any features that would make it more interesting for you!

[Bartosz Jedrzejewski @e4developer]

I think we did a pretty good job at MSL 😎

[Arena.ai @arena]

GPT-5.5 by @OpenAI is now live in the Arena, landing across multiple leaderboards.

Here’s how it ranks by modality:

- Code Arena (agentic web dev): #9, a strong +50pt jump over GPT-5.4
- Document Arena (analysis & long-content reasoning): #6, on par with Sonnet 4.6
- Text Arena: #7, Math #3, Instruction Following: #8
- Expert Arena: #5
- Search Arena: #2
- Vision Arena: #5

Strong, well-rounded performance, especially in Code (+50 pts vs GPT-5.4).

Congrats to @OpenAI on the release. Full category breakdowns by modality in the thread.

[Bartosz Jedrzejewski @e4developer]

I’ve never had as much fun being software engineer as I’m having now. The speed of turning ideas into concrete work is something else!

[BattleCastGG @BattleCastGG]

I have simulated 6.8 million battles to find the strongest CR1 monster...
I have been in a crazy rabbit hole over the past month trying to build as complete as possible D&D simulator. I think I am in a good place where most basic things and tactics work pretty well...
So i have decided to do the think I always wanted - run crazy scale D&D simulations! Hope you enjoy - https://t.co/1Vg1C9MdbX
Let me know if you have other "D&D science experiments" ideas!

[Bartosz Jedrzejewski @e4developer]

@Pack_Tacticss Okay, good point- need to implement flight and work on my dragons intelligence. Thanks once again for taking time to share feedback! 🐉

[Bartosz Jedrzejewski @e4developer]

@Pack_Tacticss I got the real art from fan content license as its a fully free thing. For AI art do you mean maps?

Will add the initiative tracker visible somewhere. Thanks for giving it a look!

[Bartosz Jedrzejewski @e4developer]

@ColbyPoulson really awesome youtube channel! I thought you may be interested in https://t.co/o2CnI5a5Mi - free D&D battle simulator I wrote (it turns out that about 10 cats are a fair fight for lvl1 wizard). Let me know if you like it!

[Bartosz Jedrzejewski @e4developer]

Also - Kobolds are just the best!

[Bartosz Jedrzejewski @e4developer]

I kept asking ChatGPT and Claude who would win D&D battles. Different models gave different answers. The same model changed its mind if I asked again.

So I built the thing myself - a grid-based combat simulator with 317 monsters, real 5e rules, and 10,000-trial Monte Carlo analysis. Three weeks of evenings and weekends. It hit #1 on r/dndnext.

A year ago this would have taken months. I wrote about how AI coding tools changed the equation - and where they didn't help at all (Reddit to the rescue!).

Try it: https://t.co/hb2mPeUgEF

Read the full story: https://t.co/6uDfQ6IJSw

[BattleCastGG @BattleCastGG]

10 Cats vs 1 lvl 1 Wizard is a pretty balanced fight in D&D!

You can try other matchups on https://t.co/phPluFE591

#DnD #DnD5e #DMTools

[BattleCastGG @BattleCastGG]

After amazing feedback from the Reddit post - https://t.co/GuYBtFuNXG I have been crazy busy implementing dozens of fixes. The simulation is getting quite stable and reliable now!

[BattleCastGG @BattleCastGG]

It takes about 8 Hobgoblins to make a fair fight against a Level 6 Barbarian.

10,000 simulations. 54/46 win rate.

What matchups do you want to see?

https://t.co/hxY1t0l9tq

[Bartosz Jedrzejewski @e4developer]

I've been building BattleCast (https://t.co/T2xAkBpBIe) - a D&D 5e combat simulator where you watch the battles play out on a grid.

82 SRD monsters, different tactics, Monte Carlo win probability analysis, animated replays. All in the browser.

Very early stage - feedback welcome!

[Alexandr Wang @alexandr_wang]

okay this is too exciting :)

meta AI is now #2 in the app store, top AI app!

we are so back!

[Han Fang @Han_Fang_]

@alexandr_wang It’s #1 in the productivity category now

[Jack Wu @JackTripleU]

Go open Meta AI app -> Do something fun -> Create an arcade game -> reply here with the result!

[Bartosz Jedrzejewski @e4developer]

Proud to have been a part of this journey! This is just the beginning 😎⚡️

[Alexandr Wang @alexandr_wang]

1/ today we're releasing muse spark, the first model from MSL. nine months ago we rebuilt our ai stack from scratch. new infrastructure, new architecture, new data pipelines. muse spark is the result of that work, and now it powers meta ai. 🧵