The 150K upgrade to Aspire was in both our accounts for MONTHS then disappeared.

We went on a month long international trip and got back on late night Thanksgiving Day. On Saturday when I finally got around to look at card activities etc I saw a 150K upgrade to Ascend offer sitting in my AMEX offers under the no fee Hilton card. Husband's offer remains to Aspire.

Given the Aspire 150K upgrade has been in and out at least 3 times I dont see it will go away anytime soon.

I may bite the 150K Ascend upgrade in late Dec when ready to pay some bills but not now.

UPDATE
Received an email for Ascend 150K upgrade offer for husband's account. His was to Aspire shown in his AMEX online as recent as 2 days ago. Now he received the 150K Ascend offer.
There is no mentioning of expiration date either in the email or on the offer landing page (which requires you to log in to go further).
A friend who was not eligible for Ascend upgrade before, now found he was eligible thru the offer page after he logged in.