The Sony Xperia M4 Aqua has seen its first update in a while, although it doesn’t look like a big firmware update. Build number 26.1.A.2.147 has been certified for the single SIM Xperia M4 Aqua models, which compares to current version number 26.1.A.2.99.
Likewise the Xperia M4 Aqua Dual has seen build number 26.1.B.2.129 certified, from version 26.1.B.2.102 currently. Don’t expect this to be Android 5.1, but hopefully it will include a full fix for the Stagefright exploit.
Xperia M4 Aqua build number 26.1.A.2.147 certified for E2303, E2306, E2353 variants
Xperia M4 Aqua Dual build number 26.1.B.2.129 certified for E2312, E2333, E2363 variants