ACCELERATE_BYPASS_DEVICE_MAP is the only boolean env flag read case-sensitively, so =True is silently ignored

Start in src/accelerate/accelerator.py at the three ACCELERATE_BYPASS_DEVICE_MAP reads identified at lines 1475, 1816, and 1890, and compare them with the sibling boolean flags that lowercase values. Done means True and TRUE behave like true at all three sites without changing the behavior of values accepted today.

Describe the bug

ACCELERATE_BYPASS_DEVICE_MAP is the only boolean environment flag in accelerate that is read case-sensitively, so setting it to True silently does nothing while the identical spelling works for every sibling flag.

All three read sites in src/accelerate/accelerator.py compare without .lower():

# accelerator.py:1475, 1816, 1890
os.environ.get("ACCELERATE_BYPASS_DEVICE_MAP", "false") != "true"

Every other boolean flag lowercases first. Sweeping src/accelerate for boolean env comparisons:

Ten of eleven are case-insensitive. The eleventh is the escape hatch.

Reproduction

The expressions as written in accelerator.py, side by side:

def bypass_active(v):   # accelerator.py:1475 / 1816 / 1890
    return not (v != "true")

def fsdp_active(v):     # accelerator.py:381 and 9 sibling sites
    return v.lower() == "true"

value    BYPASS_DEVICE_MAP   USE_FSDP (sibling)
'true'   True                True
'True'   False               True
'TRUE'   False               True

Why it matters

The variable is an escape hatch, and both of the things it guards fail quietly when it is ignored:

1. accelerator.py:1475 raises ValueError("You can't train a model that has been loaded with device_map='auto' in any distributed mode. ..."). A user who sets ACCELERATE_BYPASS_DEVICE_MAP=True still gets the exception, and the error text does not mention the variable, so there is nothing to suggest the value was the problem.
2. accelerator.py:1890 selects DDP device_ids / output_device. Ignored here, the process silently takes the non-bypass branch.

The variable is undocumented, so it is learned from issues and discussions where capitalisation is not consistent, and True is the spelling a Python user reaches for first. It is also the spelling that works for ACCELERATE_USE_FSDP in the same file, which makes the inconsistency actively misleading rather than merely strict.

Expected behavior

ACCELERATE_BYPASS_DEVICE_MAP should be read the same way as its ten siblings. Adding .lower() at the three sites only widens acceptance to True and TRUE, so no value that works today changes meaning.

A related question, deliberately kept separate

None of these eleven flags accept 1, yes, or on, even though str_to_bool in utils/environment.py is the library's own documented truth parser and accepts all of them. Routing the flags through str_to_bool would make the whole family consistent, but that is a larger change with a wider blast radius, so I have not folded it in here. Happy to open it separately if it is wanted.

Checked before filing

Searched the tracker, issues and pull requests, open and closed, for ACCELERATE_BYPASS_DEVICE_MAP and BYPASS_DEVICE_MAP; nothing found. Present on main at f13f7c1 (v1.16.0dev), all three sites.

I have the one-line fix ready and am happy to open the PR if you would like it.